What is vitamin D good for? Most people believe that the function of vitamin D is mostly confined to regulating absorption of calcium and phosphorus, making it a very important nutrient when it comes to bone and muscle health. But the sunshine vitamin has much more to offer beyond this classic and well-known role in calcium metabolism. In fact, it is one of the most important nutrients that you need to be able to sustain optimal health and well-being.
Studies show that vitamin D plays an integral role in regulating immunity, lowering inflammation and maintaining a healthy cardiovascular system.
Vitamin D Receptors
Did you know that almost every cell in your body contains receptors for vitamin D? Whether it is immune cells or cells in your brain, heart, bones, lungs, breasts, intestines, muscles and even your thyroid gland, nearly all cells have these specialized receptors called Vitamin D receptors, or VDRs. The active form of vitamin D gets attached to these VDRs. These vitamin D activated receptors then help promote expression of genes that are responsible for all kinds of wide-ranging functions and biological processes.
In the intestines, these vitamin D bound receptors facilitate the expression of genes that absorb calcium and phosphorus. In the immune cells, these receptors help express genes that trigger the formation of natural antibiotic proteins to ward off foreign invaders that might cause infections and disease.
While you may think low vitamin D levels give you weak bones and painful muscles, research suggests that vitamin D deficiency is a risk factor for many chronic health conditions, such as autoimmune diseases, metabolic disorders, infections, heart disease, cognitive impairment, depression, and even some types of cancers.  The majority of the pregnant women today are vitamin D deficient, exposing their unborn babies at all kinds of health risks including allergies, asthma, wheezing disorders and even autism.
Illnesses Associated with Low vitamin D Levels
Your body can make its own vitamin D with adequate exposure to sunlight. But decreased sun exposure – mostly due to lifestyle changes such as spending less time outdoors due to work, lack of physical activity, fear of developing skin cancer and excessive use of sunscreen – has significantly contributed to vitamin D deficiency on a global scale.
Are you diagnosed with low levels of vitamin D? You may be at risk of developing these health conditions:
- Respiratory infections
Your immune system is your best defense in fighting infections and keeping diseases at bay. And vitamin D plays a very important role in bolstering your immune system through the production of natural anti-bacterial proteins in the body. These antimicrobial proteins help the body fight a wide range of infections including cold, flu and asthma and even tuberculosis. Not surprisingly, many of your immune cells such as monocytes, macrophages, dendritic cells, T cells, and B cells have receptors for vitamin D and the enzymes required to convert the circulating vitamin D into active vitamin D.  
In addition to its positive role in strengthening natural immunity, vitamin D also works as an anti-inflammatory and improves lung functions.  These properties make vitamin D supplements a highly effective strategy in managing asthma and preventing acute respiratory tract infections, such as cold and flu, that have the potential to trigger and aggravate asthma attacks.
For example, a 2017 study found that vitamin D is effective against acute respiratory infections such as colds and flu, although it emphasized that supplements work best for people with severe vitamin D deficiency. . Vitamin D was also found to be more useful in flu prevention than anti-viral drugs and vaccines .
- Heart Disease
Low vitamin D levels are associated with an increased risk of heart failure, heart attack, stroke and peripheral arterial disease.  It also contributes to other factors considered high risk for heart disease, such as high blood pressure and diabetes.
While low levels increase your risk, could improving your levels with vitamin D supplements help in preventing heart disease risk? Vitamin D seems to be doing a lot of hard work when it comes to maintaining heart health and minimizing risks that are directly related to cardiovascular disease. For example, vitamin D lowers inflammation, reduces vascular stiffness, lowers blood pressure and improves endothelial functions . Daily supplementation with vitamin D also improves heart functions in patients suffering from chronic heart failure .
One study found that vitamin D may help reverse the damage inflicted on the endothelium in several diseases such as high blood pressure, diabetes and atherosclerosis. The study found that vitamin D stimulates the production of nitric oxide, a molecule that regulates blood flow, endothelial health and blood clot formation in the blood vessels. Vitamin D also reduces oxidative stress in the cardiovascular system.
The study concluded that, “This effect of vitamin D3 may prove to be beneficial in the treatment of hypertension and other cardiovascular diseases, including heart failure, myocardial infarction, vasculopathy, stroke and diabetes.”  “There are not many, if any, known systems which can be used to restore cardiovascular endothelial cells which are already damaged, and Vitamin D3 can do it,” Malinski, the lead researcher said. “This is a very inexpensive solution to repair the cardiovascular system. We don’t have to develop a new drug. We already have it.” 
- Autoimmune Disorders
Your immune system is designed to protect you from infections and disease. In autoimmune disorders, the immune system becomes hyper-responsive and starts attacking its own healthy tissues, leading to tissue inflammation and damage. While genetics and environmental factors play a key role in the development of autoimmune diseases, deficiency in vitamin D could be an important (and often overlooked) player.
Studies suggest a positive association between low vitamin D levels and increased risk of autoimmune diseases, such as Multiple Sclerosis, lupus, type 1 diabetes, rheumatoid arthritis (RA) and inflammatory bowel disease (IBD) .
Vitamin D has a dual effect on the immune system functioning. On one hand, it bolsters the natural immunity through its ability to stimulate the production of natural antibiotics, which helps fight infections. On the other hand, vitamin D has a regulatory effect on the adaptive immunity, a part of your overall immunity that helps launch the body specific immune responses through a specialized army of B cells and T cells.
Vitamin D increases the number and functions of T regulatory cells (Tregs), one of the T cells.   . Tregs are specifically responsible for differentiating between the foreign invaders and the body’s own healthy cells and tissues. Treg cells help build immune tolerance by suppressing untoward reactions of other immune cells. By increasing this suppressive function of Treg cells, vitamin D prevents inappropriate immune responses that cause an autoimmune disease.
- Type 2 diabetes
Poor vitamin D status has been linked to obesity and type 2 diabetes. A recent study found that individuals with healthier levels of vitamin D in their blood have lesser risk of developing type 2 diabetes than those with lower levels. . This is not the first study to make this association. However, more research is needed to duplicate the findings and confirm this relationship between low vitamin D levels and higher incidence of diabetes.
While the precise mechanism through which higher levels lowers the risk of type 2 diabetes is not yet clear, this is believed to be due to vitamin D’s role in improving insulin sensitivity and reducing inflammation. A 2016 study put forth another interesting mechanism that vitamin D regulates energy and glucose metabolism through its direct actions in the brain. It appears that we have vitamin D receptors or VDRs in the hypothalamus, a part of the brain well-known to control both body weight and glucose. 
- Thyroid issues
Studies show that vitamin D deficiency increases the risk of autoimmune thyroid disorders such as Hashimoto’s and Grave’s disease.   (In Hashimoto’s, the immune system makes antibodies that attack the thyroid gland, causing inflammation and reduced production of thyroid hormones. In Grave’s disease, the immune system makes antibodies that stimulate the thyroid gland to produce more thyroid hormones that you need.)
A 2017 study showed that healthy vitamin D levels are needed to maintain normal thyroid functions. . In addition, you need vitamin D to make T3 hormone available for the cells. Your thyroid gland produces T4 and T3 hormones. T4 is converted into T3, which performs its functions inside the cells. Now, T3 first needs to bind to the receptors of the cells so that it can become active and available for use. You need sufficient levels of vitamin D for this critical step.
If sensible sun exposure (during mid-day when your shadow is not taller than you are) is not an option for you to make vitamin D naturally, you need to top up your levels with a high quality liposomal vitamin D. You also need to remember that taking too much vitamin D could also be dangerous, so the correct dosage is important. Vitamin D intake also creates a need for magnesium and vitamin K2. You need magnesium to efficiently use vitamin D and vitamin K2 to prevent calcium deposition in arteries and soft tissues.
- Wang et al. Vitamin D and Chronic Diseases. Aging Dis. 2017.
- Adrian F Gombart. The vitamin D–antimicrobial peptide pathway and its role in protection against infection. Future Microbiology. 2009
- Youssef et al. Antimicrobial implications of vitamin D. Dermatoendocrinol. 2011
- Hooman Mirzakhani et al. Vitamin D and the development of allergic disease: how important is it? Clin Exp Allergy. 2015.
- Martineau et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ, 2017
- Mitsuyoshi Urashima, Takaaki Segawa, Minoru Okazaki, Mana Kurihara, Yasuyuki Wada, and Hiroyuki Ida. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 2010
- Erin Michos. Vitamin D and the Heart. Heart and Vascular Institute. Johns Hopkins Medicine.
- Ioana Mozos, Otilia Marginean. Links between Vitamin D Deficiency and Cardiovascular Diseases. BioMed Research International. 2015
- Vitamin D improves heart function, study finds. Science Daily. University of Leeds, 2016
- Khan et al. Nanomedical studies of the restoration of nitric oxide/peroxynitrite balance in dysfunctional endothelium by 1,25-dihydroxy vitamin D3 – clinical implications for cardiovascular diseases. International Journal of Nanomedicine. 2018.
- Malinski’s Study Shows Vitamin D3 Could Help Heal, Prevent Cardiovascular Damage. Ohio University.
- Prietl B et al. Vitamin D and Immune Function. Nutrients. 2013.
- Prietl B et al. Vitamin D supplementation and regulatory T cells in apparently healthy subjects: vitamin D treatment for autoimmune diseases? Isr Med Assoc J. 2010.
- Siklar et al. Regulatory T Cells and Vitamin D Status in Children with Chronic Autoimmune Thyroiditis. J Clin Res Pediatr Endocrinol. 2016
- Gorman et al. Dietary Vitamin D Increases Percentages and Function of Regulatory T Cells in the Skin-Draining Lymph Nodes and Suppresses Dermal Inflammation. Journal of Immunology Research. 2016.
- Park et al. Plasma 25-hydroxyvitamin D concentration and risk of type 2 diabetes and pre-diabetes: 12-year cohort study. PLoS One. 2018
- Sisley et al. Hypothalamic Vitamin D Improves Glucose Homeostasis and Reduces Weight. Diabetes. 2016
- Tamer et al. Relative vitamin D insufficiency in Hashimoto’s thyroiditis. Thyroid. 2011
- Mazokopakis et al. Is vitamin D related to pathogenesis and treatment of Hashimoto’s thyroiditis? Hell J Nucl Med. 2015
- Mirhosseini et al. Physiological serum 25-hydroxyvitamin D concentrations are associated with improved thyroid function—observations from a community-based program. Endocrine. 2017